Ta có :

B = 2 . 4 . 6 + 4 . 6 .8 + ......+ 96 .98 .100

B.8 = 2 . 4 . 6 . 8 + 4. 6 . 8 .( 1 0 - 2) +........+96 . 98 . 100 . ( 102 - 94 )

8B = 2 . 4 . 6 .8 + 4. 6 .8 . 10 - 2 . 4 . 6 . 8 +......+ 96 . 98 . 100. 102 - 94 . 96 . 98 . 100

8B = 96 . 98 . 100 . 102

B = 96 . 98 . 100 .1 02 : 8

B = 12 . 98 . 100. 102

tôi mới lên lớp 5 thôi nên  ko có biết !!!

sorry nha

\(A=\frac{2}{2.4.6}+\frac{2}{4.6.8}+\frac{2}{6.8.10}+\frac{2}{8.10.12}\)

\(A=\frac{2}{48}+\frac{2}{192}+\frac{2}{480}+\frac{2}{960}\)

\(A=\frac{1}{24}+\frac{1}{96}+\frac{1}{240}+\frac{1}{480}\)

\(A=\frac{20}{480}+\frac{5}{480}+\frac{2}{480}+\frac{1}{480}\)

\(A=\frac{7}{120}\)

A = \(\dfrac{2}{2.4.6}\) + \(\dfrac{2}{4.6.8}\) + \(\dfrac{2}{6.8.10}\) + \(\dfrac{2}{8.10.12}\)

A = \(\dfrac{2}{2}\).(\(\dfrac{2}{2.4.6}\) + \(\dfrac{2}{4.6.8}\) + \(\dfrac{2}{6.8.10}\) + \(\dfrac{2}{8.10.12}\))

A = \(\dfrac{1}{2}\).(\(\dfrac{2.2}{2.4.6}\) + \(\dfrac{2.2}{4.6.8}\) + \(\dfrac{2.2}{6.8.10}+\dfrac{2.2}{8.10.12}\))

A = \(\dfrac{1}{2}\).( \(\dfrac{4}{2.4.6}+\dfrac{4}{4.6.8}+\dfrac{4}{6.8.10}+\dfrac{4}{8.10.12}\))

A = \(\dfrac{1}{2}\).(\(\dfrac{1}{2.4}\) - \(\dfrac{1}{4.6}\) +\(\dfrac{1}{4.6}\) - \(\dfrac{1}{6.8}\) + \(\dfrac{1}{6.8}\) - \(\dfrac{1}{8.10}\) + \(\dfrac{1}{8.10}\) - \(\dfrac{1}{10.12}\))

A = \(\dfrac{1}{2}\).(\(\dfrac{1}{2.4}\) - \(\dfrac{1}{10.12}\))

A = \(\dfrac{1}{2}\).(\(\dfrac{1}{8}-\dfrac{1}{120}\))

A = \(\dfrac{1}{2}\).\(\dfrac{7}{60}\)

A = \(\dfrac{7}{120}\)